Purification of waters, whether surface or waste, has been the object of numerous studies that have led to the development of processes that can be grouped, in a summary fashion, as follows:
(a) processes of coagulation-flocculation-decantation-filtration on sand (on surface);
(b) also purely mechanical filtering processes, but in the mass;
(c) so-called biological filtering processes, simultaneously resorting to the action of microorganisms assuring degradation of the organic impurities contained in the water;
(d) processes of adsorption on activated carbon, after flocculation-decanting and possibly filtering on sand;
(e) treatments with activated sludge;
(f) treatments with bacterial beds.
It can be said that each of these techniques has its own advantages and drawbacks, without any of them being totally satisfactory, so that it is often necessary to combine them and thus use complex and costly treatment lines.
Without going into the details of the successive operations that water has to undergo to treat it, it can be said overall that most of these processes require the use of rather voluminous bulky equipment arranged in series so that the total treatment time can come to several hours.
To overcome these drawbacks, there was proposed in U.S. Pat. No. 4,076,616 a process of type (c) to eliminate pollution biologically in a carbon bed, according to which there is injected in this bed a gas containing oxygen to supply to the microorganisms developing in this bed the oxygen that they require. Thus, thanks to the combination of a depth filtration and the use of constantly aerated activated carbon, more complete treatment is performed in a few minutes in a single compact work.
In the process which is the object of said patent, limitations were introduced for parameters such as, for example, the time of contact of the water to be treated with the activated carbon and the linear speed of the water through the bed. In fact, it was stated that this speed should not exceed 2 m/hour to keep intact the "connective tissue" formed by the bacterial colonies that develop between the carbon particles and thus contribute to purification of the water while retaining the particles in suspension in this water.